America's Hardest Workout Classes

Yoga Revolution

A three-hour Spinning class that simulates climbing Mount Everest? Might be a bit much for us mere mortals, but if you are looking for a real challenge, we've found four tough-as-nails classes that'll give you the sky-high calorie burn you crave. Even if they're too over-the-top for you, just reading about them might inspire you to kick up your own workout a notch or five. (If you don't happen to live near a gym that offers any of these classes, we've found DVDs that promise a similar challenge.) Don't say we didn't warn you!

Yoga Revolution

Try It At: Crunch Fitness Clubs, New York City

The Benefit: Adding weights to traditional yoga moves gives your muscles more of a challenge.

Calories Burned: 400 to 500

Fitness instructor Suzi Teitelman teaches a flowing 60-minute yoga class using concave, plate-shaped, 6-pound weights called Smart Bells that challenge your balance while toning your muscles. She adds weights to all poses, including sun salutations, tree pose, and even pigeon pose. The additional resistance boosts the sculpting benefits of any pose, she says.

Signature Move: Weighted Boat Pose

Sitting on the floor with knees bent, lean back 45 degrees to engage abdominals. Lift shins parallel to floor and balance Smart Bells (or light dumbbell) across the tops of both lower legs, arms extended. Sit up tall and extend both arms toward toes, breathing deeply for 30 to 60 seconds.

At Home: Try Smart Bells Fusion DVD, $19.95 (or $74.95 with a 3-pound Fusion Smart Bell) at smartbells.com.